Time after time in serious and other fanfics, I see Tendo Kasumi say, 

"Oh My."

What are the words in Japanese?  What do they literally mean?
What is their use and translation such that english translators 
have settled on "Oh My"?

What she actually says is "maa" ... it's just a sound word, more than
anything... Sort of means the same as "oh"...

Kun-chan...